Various types of modulating valves, such as incrementally positionable valves, are widely used in refrigerant circuits for refrigeration and air-conditioning systems. For instance, modulating valves are frequently used at nodes of diverging loops of circuits to provide refrigerant for heat reclaim or for defrosting evaporators of refrigeration display units. Such valves are also used in split condensers and hot-gas applications. These valves are used to control the ratios of refrigerant conveyed to the various elements of the circuits or to control the flow of refrigerant through the lines. The modulating action of the valves prevents water hammer in the refrigerant lines, which could have adverse effects on the various elements of such circuits. Mueller™ Refrigeration Co. provides such modulating valves, under the name Cycle Master™.
However, the modulating valves of refrigerant circuits are subjected to the harsh conditions typical to circuits. For instance, the refrigerant in refrigerant circuits is at relatively high temperatures and fluctuates between large temperature variations. Furthermore, the refrigerant is compressed to relatively high pressures, and the modulating valves are often employed to create pressure drops in the circuits. Finally, the refrigerants typically known and used are often of a corrosive nature.
For these reasons, some modulating valves have been known to leak at the stem. A plurality of negative effects results from such leaks. For instance, substantial losses of refrigerant can cause inefficient refrigeration cycles and shutdowns. Furthermore, the refrigerants are often harmful to the environment, and refrigerant losses to the environment must be prevented. Finally, downtimes are very costly and are risky as the contents of the refrigeration display units cannot be subjected to temperature increases without the risk of being fouled.